Axons regenerated through silicone tube splices. II. Functional morphology.

The recovery of axons regenerated through silicone tube splices was studied with electron microscopic and morphometric methods. Regenerated nerves contained both myelinated and unmyelinated axons of near normal morphology. The number and diameter of axons increased with postoperative time, and size-frequency histograms demonstrated that regeneration occurred in all major fiber groups. Remyelination occurred between about 4 and 6 weeks. Some of the smallest regenerated axons had unusually thick myelin sheaths, but overall regenerated axons had a slightly thinner sheath compared with similar-size normal fibers, although the ratio of sheath thickness to axon size was within the normal limits of g = 0.65 to 0.8 by 6 weeks. Axons did not, however, regain their normal size within 10 months of surgery. This deficit was apparently the primary factor limiting conduction velocity in these regenerated axons.